The Cretaceous Period was the final eminent time span of the Mesozoic Age. The period denoted the dinosaurs as well as their reptilian cousins’ end of dominance in the oceans and air. Although the Jurassic Era was quiet geologically, the topography of the Cretaceous Period saw a remarkable rebirth of tectonic plate movements (Holmes 21). Continental drift during this era led to the persistent division of the northern and southern supercontinents of Laurasia and Gondwana, splitting them into landmasses resembling their current structure. The Atlantic Ocean expanded and immersed the land bridges that previously linked North America to Europe and South America to Africa. India split from Gondwana and started its northerly drift towards Asia. North America was separated by an enormous inland sea that divided the continent from the northwest Arctic to the Gulf Mexico.
The Cretaceous was the warmest time in the history of Earth because of vigorous volcanism linked to oddly high levels of seafloor diffusion. The poles were lacking ice, and average temperatures of up to 35 degrees Celsius existed in the oceans (Hu 3). The thermal gradient from equator to pole was highly decreased, and terrestrial states were equal at higher latitudes. In addition, during the early Cretaceous, the climate cooled from the Beriasian through the Valanginian with the coolest temperatures in the early Hauterivian. Later, warming ended in the early Barremian and related to the Parana-Etendeka volcanic province. High rates of warming during the late Berremian were at the utmost greenhouse conditions during early Aptian, probably connected to the Ontong Java 1 volcanic province (Keller 765). The climate was cool in late Aptian and early Albian. Warming in the Cenomanian was at the highest marine surface temperatures (28 degrees Celsius) for the Cretaceous in high southern latitudes at the beginning of Turonian (Keller 766). Warm and lower temperatures (24 degrees Celsius) existed throughout the Turonina and Coniacian. During the Santonian through early Campanian, there were warm but changing climate conditions, followed by sudden cooling of surface waters in early Campanian. Steady cooling extended throughout Maastrichtian and ended with a temporary and sudden greenhouse warming 200–400 ky before the end of the Maastrichtian (Keller 765). Afterwards, there was gradual cooling within the Cretaceous-Tertiary (K-T) border. The end-Cretaceous greenhouse warming was linked to Deccan volcanism (65–66 Ma), the Chicxulub effect, and harsh biotic stress circumstances among planktic foraminifera that resulted in the K-T mass extinction (Keller 766).
The environment evolved to the extent that flowering plants (angiosperms) started showing up for the first time. Additionally, the process increased insect pollination. Moreover, the landmasses split into continents that would be distinguished today though in different locations compared to where they are observed today. The cool climate altered the flora and plant life. Nonetheless, as it reached about 125 ma, the climate started warming partly because of the volcanic activity as well as high rates of carbon dioxide in the air (Hu 2).
Apart from Dinosaurs, other animals existed in the Cretaceous Period, which fought for space and food. There were amphibians, such as frogs and nets that evolved continuously and diversified. The reptiles included turtles, snakes, crocodiles, and lizards. The flying animals were the pterosaurs, birds, and several winged insects (Barnes-Svarney and Svarney 107). The biggest flying animal was the Quetzalcoatlus, a late Cretaceous Period pterosaur discovered in Texas, and its size was equal to current small airplanes.The avians multiplied and broadly diversified in the Cretaceous era. The Confuciusornis used to be a crow-sized bird with a contemporary beak, but huge claws at the ends of the wings. Iberomesornis, which the same size as a sparrow, could fly and was an insectivore.
Towards the end of the Jurassic, various large sauropods, such as Apatosaurus and Diplodocus were nonexistent. However, other giant sauropods, which include the titanosaurs, thrived near the end of the Cretaceous (Holmes 137). Several animals that depended only on plants for food also survived and multiplied during the Cretaceous period. Mammals lived in the Cretaceous Era although they were insignificant. The first mammals were very small organisms than the giant dinosaurs. Tyrannosaurus Rex, which was the highly renowned dinosaur, existed in the Cretaceous Era and reigned the land when the period ended. The dinosaurs flourished and multiplied in the Cretaceous because of a revolution of life that happened at that time. It occurred as various kinds of present flora and fauna appeared for the first time. The growth and supremacy of flowering plants together with the emergence of new sorts of insects offered dinosaurs good sources of food (Barnes-Svarney and Svarney 86). The ancestors of current grebes, cormorants, pelicans, and sandpipers appeared in the Cretaceous (Holmes 158).
Among the features of the Cretaceous Era was the growth and rays of the flowering plants (angiosperms). They included the forebears of the beech, fig, magnolia, and sassafras. There were many plants towards the end of the Cretaceous. The lower Cretaceous is marked by a revolution (Bond and Scott 1138)
Approximately 65.5 million years ago, almost all large vertebrates, as well as several tropical invertebrates, vanished in a geological climate and biological occurrence with global effects (Friedrich, Norris, and Erbacher 108). Geologists refer to it as the K-Pg extinction incident since it indicates the boundary between the Cretaceous and Paleogene Eras. The occurrence was initially called the Cretaceous-Tertiary (K-T) incident. It is believed that a meteor struck the earth in the Gulf of Mexico off the Yucatan Peninsula. The process led to the formation of several geologic activities. The volcanoes exploded, and clouds, smoke as well as dust enclosed the skies, preventing the sun’s light from reaching the planet for a long time. This process led to enormous variations in climate and vegetation.
The splitting of Africa and South America formed an extended sequence of volcanic mountains undersea. The mountains expanded as the Atlantic Ocean became broader and displaced a lot of water, making the level of the seas higher compared to the preset. This process led to the creation of various internal oceans. Moreover, in some parts of the world, the internal oceans divided the continent into segments that became different countries.
The sudden disappearance of Cretaceous life is still a mystery. The theories of extinctions relate it to severe cooling of the globe, the departure of the seas, separation of the continents, biological illness, turnarounds of the earth’s magnetic field, or a variation in atmospheric carbon dioxide and oxygen. Nevertheless, Luis and Walter Alvarez and associate, at the University of California, pioneered the broadly acknowledged theory in 1980. The researchers stated that an asteroid punched the earth, polluting the air with dirt. This process interfered with photosynthesis and made it hard for organisms to survive on each other. The proof of the impact entails an irregular iridium layer similar to meteorites and craters that occurred in the late Cretaceous.
Experts affirm that the end of Cretaceous is associated with gigantic volcanic outbreak. One version has combined the two theories, postulating that shock waves from the effect of a large asteroid moved through the earth, trembling its crust, and activating or strengthening the volcanic incidents. A different theory suggests that the magma movements initiated several incidents, which damaged organisms that lived in water many years before the dinosaurs were terminated. Numerous species that endured did not rely much on plant life. The insects outlived on other animals as well as dead creatures and mammals normally fed on insects. The process enabled mammals to live until today and substituted dinosaurs as the domineering species (Keller 169).
Among the significant developments in the Cretaceous Period was the evolution of flowering plants, as trees started generating flowers and not cones. The Cretaceous was a difficult time era in Earth’s history, which witnessed incidents of sudden greenhouse warming and cooling, key digressions in carbon isotope history, occasional oceanic anoxic incidents, and higher rates of volcanic activities that developed large igneous provinces. The Cretaceous Period was warm, and the poles were cooler than the lower attitudes. However, it is probable that towards the end of the period, some irregular zones of climate had appeared, causing the general climate to be cooler. The variations together with the alterations in the earth’s surface and its flora and fauna ended the Mesozoic era.
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